Traditionally, absorbent articles such as diapers comprise an absorbent core with water-absorbent (cellulose) fibers and particles of superabsorbent polymer particle, also referred to as particles of absorbent gelling material (“AGM”), enclosed by a substrate material, or supported by a substrate material and then closed by a further material, e.g. such as a nonwoven.
Absorbent articles with so-called profiled absorbent cores have been developed, whereby certain regions of the article comprise more AGM than other regions. In such instances, accurate deposition of AGM is important to obtain the required profile. Furthermore, in the case of absorbent cores with only small amounts of, or no, cellulose fibers (having thus AGM particles as the only liquid storage material) accurate AGM distribution is highly important.
Various approaches have been proposed for obtaining absorbent cores with primarily AGM particles and for obtaining absorbent cores that have AGM particles in a specific profile or distribution, such as a predetermined pattern, thickness profile, or adjusting various components of the manufacturing apparatus that act in the machine direction (“MD”), or cross-direction (“CD”). These approaches include indirect printing methods, whereby the AGM particles are taken up by a drum from a bulk storage of AGM particles—said roll or drum having reservoirs on the surface thereof, the number, size and position of which determining the amount and pattern of AGM granules taken up by the drum- and whereby the drum then rotates towards a substrate such as a nonwoven, to then release the AGM onto the substrate (carried by a moving surface).
Surprisingly, the inventors found that such proposed indirect printing processes are in some instances difficult to run at high speed, for example at speeds of more than 800 ppm or more than 1000 ppm (parts (absorbent cores) per minute), in particular when fine particulate material is used and/or when small (and large quantities of) reservoirs are used. It has been found that at high speeds, the AGM particles are not always satisfactorily dropped (e.g. from a feeder/hopper) into the reservoirs of the roll/drum. Reservoirs may only be partially filled, whilst at certain areas of the drum excess AGM may build up. If vacuum (in the roll/drum) is used to aid filling of the reservoirs, then this AGM build-up may obstruct the vacuum suction and this it may further obstruct the filling of the reservoirs This thus may result in an inaccurate distribution of the AGM in the absorbent cores, or even defects in the formed absorbent cores.
The inventors have now found an improved apparatus and method for producing, even at high speed, (absorbent) structures comprising particulate (absorbent) material; said apparatus and method are furthermore able to employ a moving surface (e.g. roll or drum) with a large number of small reservoirs, whilst still delivering accurate filling.